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Xu Li

Publications and source records attributed to Xu Li.

At least 37 records · Page 2Linked to original sources
PubMed2006

Expression, purification, crystallization and preliminary X-ray diffraction analysis of human phosphoribosyl pyrophosphate synthetase 1 (PRS1).

Phosphoribosyl pyrophosphate synthetase (PRS; EC 2.7.6.1) catalyzes the reaction of ribose-5-phosphate (R5P) with ATP to yield AMP and PRPP (5-phosphoribosyl-1-pyrophosphate), which is necessary for the de novo and salvage pathways of purine-, pyrimidine- and pyridine-nucleotide biosynthesis. PRPP is a metabolite that is required at all times in the cell and is thus central to life. In this study, human PRS1 was produced in Escherichia coli in soluble form and purified to homogeneity. Crystals in complex with Mg2+, inorganic phosphate (P(i)) and ATP were obtained by the hanging-drop vapour-diffusion method. Diffraction data were collected to 2.6 A resolution. The crystal belongs to space group R3, with unit-cell parameters a = b = 168.846, c = 61.857 angstroms, assuming two molecules in the asymmetric unit and a volume-to-weight ratio of 2.4 angstroms3 Da(-1), which was consistent with the result calculated from the self-rotation function.

Brain↗
PubMed2006

Self-assembled supramolecular hydrogels formed by biodegradable PEO-PHB-PEO triblock copolymers and alpha-cyclodextrin for controlled drug delivery.

A materials design of a new supramolecular hydrogel self-assembled between alpha-cyclodextrin and a biodegradable poly(ethylene oxide)-poly[(r)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer was demonstrated. The cooperation effect of complexation of PEO segments with alpha-cyclodextrin and the hydrophobic interaction between PHB blocks resulted in the formation of the supramolecular hydrogel with a strong macromolecular network. The in vitro release kinetics studies of fluorescein isothiocyanate labeled dextran (dextran-FITC) model drug from the hydrogel showed that the hydrogel was suitable for relatively long-term sustained controlled release of macromolecular drugs, which many simple triblock copolymer hydrogel systems could not achieve. The hydrogel was found to be thixotropic and reversible, and can be applied as a promising injectable drug delivery system.

Biocompatible Materials↗
PubMed2006

Dynamic and static light scattering studies on self-aggregation behavior of biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) triblock copolymers in aqueous solution.

The self-aggregation behavior of two amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer samples with nearly identical PHB block lengths but different PEO block lengths, PEO-PHB-PEO(2000-810-2000) and PEO-PHB-PEO(5000-780-5000), was studied with dynamic and static light scattering (DLS and SLS), in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of polymeric micelles by the two PEO-PHB-PEO triblock copolymers was confirmed with fluorescence technique and TEM. DLS analysis showed that the hydrodynamic radius (R(h)) of the monodistributed polymeric micelles increased with an increase in PEO block length. The relative thermostability of the triblock copolymer micelles was studied by SLS and DLS at different temperatures. The aggregation number and the ratio of the radius of gyration over hydrodynamic radius were found to be independent of temperature, probably due to the strong hydrophobicity of the PHB block. The combination of DLS and SLS studies indicated that the polymeric micelles were composed of a densely packed core of hydrophobic PHB blocks and a corona shell formed by hydrophilic PEO blocks. The aggregation numbers were found to be approximately 53 for PEO-PHB-PEO(2000-810-2000) micelles and approximately 37 for PEO-PHB-PEO(5000-780-5000) micelles. The morphology of PEO-PHB-PEO spherical micelles determined by DLS and SLS measurements was further confirmed by TEM.

Biocompatible Materials↗
PubMed2006

Assessments of the accumulation severities of amyloid beta-protein and hyperphosphorylated tau in the medial temporal cortex of control and Alzheimer's brains.

Alzheimer's disease (AD) is characterized neuropathologically by neuritic plaques (NPs), and neurofibrillary tangles (NFTs). So far, the following key issues are not yet answered to the disease: (1) the accumulation degrees of three Abeta variants, and tau phosphorylation epitopes in AD as compared to control; (2) the correlation degrees of levels of three Abeta variants with different tau phosphorylation epitopes; (3) the correlation degrees of levels of three Abeta variants and different tau phosphorylation epitopes with Braak and CERAD staging systems. To address these issues, levels of Abeta40, Abeta42, and Abeta43, and phosphorylated tau were assessed by dot blots in homogenates of the medial temporal cortex from AD and control brains in the present study. These data implied different roles of tau phosphorylation epitopes in formation of NFTs, and in this process, Abeta might play a key role. Assessments of levels of these abnormal proteins by dot blots may serve as a useful complement to the morphological evaluations in diagnosis of AD.

Aged↗
PubMed2006

Synthesis of large-pore methylene-bridged periodic mesoporous organosilicas and its implications.

In this article, we report the synthesis of methylene-bridged periodic mesoporous organosilicas (PMOs) of the SBA-15 type. The materials were characterized by SAXS, BET, NMR, FESEM, and TEM. It was found that the synthesis of methylene-bridged SBA-15 PMOs requires more rigorous conditions than that of SBA-15 PMOs bearing organic bridges other than methylene. A mild acidic environment, which slows down the hydrolysis and condensation rates of the precursor, with the assistance of a salt, which enhances precursor-template interaction, should be used to synthesize high-quality large-pore methylene-bridged PMOs. We attributed this to the fast hydrolysis and condensation rates and the rigid backbone of precursor 1,2-bis(triethoxysilyl)methylene. By examining and comparing the synthesis of three large-pore PMOs with different bridges, we concluded that the inductive, bridging, and conformation effects of the organic bridging group play an important role in the synthesis of large-pore PMO materials.

Magnetic Resonance Spectroscopy↗
PubMed2006

Backscattering enhancement of light by nanoparticles positioned in localized optical intensity peaks.

We report what we believe to be a novel backscattering phenomenon associated with localized optical intensity peaks (spanning as little as 43 nm) arising at the shadow-side surfaces of plane-wave-illuminated dielectric microcylinders of noncircular cross sections. Namely, for nanometer-scale dielectric particles positioned within the localized intensity peaks, their backscattering of visible light is enhanced by several orders of magnitude relative to the case of isolated nanoparticles (i.e., Rayleigh scattering). The positions of the localized intensity peaks can be quickly scanned along the microcylinder surface by changing either the incident wavelength or angle. This combination of giant backscattering enhancement of nanoparticles and ease and rapidity of scanning may present advantages relative to the use of fragile, mechanically scanned, near-field probes. Potential applications include visible-light detection, characterization, and manipulation of nanoparticles.

Light↗
PubMed2006

The possible role of EWS-Fli1 in evasion of senescence in Ewing family tumors.

The chromosomal translocation t(11;22) yields the EWS-Fli1 fusion gene and is associated with oncogenesis of Ewing family tumors (EFT). In this study, using the RNA interference method, we show that EWS-Fli1-targeting small interfering RNAs (siRNA) depleted EWS-Fli1 protein and caused growth inhibition in EFT cells with the accumulation of p27 protein and the down-regulation of Skp2 protein in dose-dependent, time-dependent, and sequence-specific manners. Depletion of EWS-Fli1 subacutely elicited a senescence-like phenotype, but not apoptosis, in EFT cells. Furthermore, not only the knockdown of p27, but also the forced expression of Skp2, reduced the expression levels of p27 protein and partially rescued senescence-like phenotype caused by EWS-Fli1-targeting siRNAs. The accumulation of p27 protein in EWS-Fli1-depleted cells inhibited cdk2 kinase activity and was related to the stability of p27 protein, which resulted from a decrease in Skp2 protein. Immunohistochemical analysis of p27 and Skp2 proteins in EFT samples revealed that there was an inverse relationship between the expression profiles of p27 and Skp2 proteins. These findings indicate an important role of EWS-Fli1 in the prevention of senescence, leading to the unlimited growth and oncogenesis of EFT cells through a decrease in the stability of p27 protein due to increased action of Skp2-mediated 26S proteasome degradation.

Apoptosis↗
PubMed2006

Superenhanced backscattering of light by nanoparticles.

We report a physical explanation for the phenomenon wherein the backscattering of light by dielectric particles of sizes between 100 and 1 nm is enhanced by 7-11 orders of magnitude. The phenomenon involves complex composite interactions between a dielectric microsphere and a nanoparticle positioned in close proximity to the microsphere. We provide both analytical and perturbation analyses that show that the enhanced backscattering intensity of a nanoparticle is proportional to the third power of its size parameter. Potential applications of this phenomenon include visible-light detection, characterization, and manipulation of particles as small as a few nanometers.

Biosensing Techniques↗
PubMed2006

Involvement of P-glycoprotein and MRP1 in resistance to cyclic tetrapeptide subfamily of histone deacetylase inhibitors in the drug-resistant osteosarcoma and Ewing's sarcoma cells.

Despite recent improvements in multimodal therapies for osteosarcoma (OS) and Ewing's family of tumors (EFTs), the prognosis of relapsed cases remains very poor because of the resistance to chemotherapy. Histone deacetylase inhibitors (HDACIs), including members of the cyclic tetrapeptide family such as FK228 and apicidin, are novel antitumor agents that can induce cell cycle arrest and apoptosis in various cancer cells. HDACIs also exhibit potent antitumor effects on OS and EFTs. However, to date there have been no studies to our knowledge reporting the effects of HDACIs on drug-resistant OS and EFTs. Here, we demonstrated that FK228 and apicidin exhibited strong resistance in doxorubicin-resistant clones of OS and EFTs expressing P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) and that P-gp and MRP1 might play a crucial role in the resistance mechanism to FK228 and apicidin. A P-gp inhibitor (verapamil) and an MRP1 inhibitor (MK571) could independently reverse the resistance to FK228 and apicidin in the drug-resistant clones. Moreover, the combination of verapamil and MK571 could enhance HDACI-induced cell number reduction in drug-resistant clones to a similar extent as that in their parental clones. Although these findings suggest the difficulty in treating drug-resistant tumors expressing P-gp and/or MRP1 with these HDACIs, the combination of P-gp and MRP1 inhibitors might reverse the resistance to the HDACIs in the treatment of those tumors. Because HDACIs are potent and promising antitumor drugs and seem to be close to clinical use, it is necessary to pay attention to the resistance mechanisms against HDACIs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Synthesis, characterization, and morphology studies of biodegradable amphiphilic poly[(R)-3-hydroxybutyrate]-alt-poly(ethylene glycol) multiblock copolymers.

Novel biodegradable amphiphilic alternating block copolymers based on poly[(R)-3-hydroxybutyrate] (PHB) as biodegradable and hydrophobic block and poly(ethylene glycol) (PEG) as hydrophilic block (PHB-alt-PEG) were successfully synthesized through coupling reaction. Their chemical structures have been characterized by using gel permeation chromatography, (1)H nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) analysis revealed that both PHB and PEG blocks in PHB-alt-PEG block copolymers can crystallize to form separate crystalline phase except in those with a short PEG block (M(n) 600) only PHB crystalline phase has been observed. However, due to the mutual interference from each other, the melting transition of both PHB and PEG crystalline phases shifted to lower temperature with lower crystallinity in comparison with corresponding pure PHB and PEG. The crystallization behavior of PHB block and PEG block has also been studied by X-ray diffraction, and the results were in good agreement with those deduced from DSC study. The surface morphologies of PHB-alt-PEG block copolymer thin films spin-coated on mica have been visualized by atomic force microscopy with tapping mode, indicating formation of laterally regular lamellar surface patterns. Static water contact angle measurement revealed that surface hydrophilicity of these spin-coated thin films increases with increasing PEG block content.

Chromatography, Gel↗
PubMed2006

Concurrent alterations of O-GlcNAcylation and phosphorylation of tau in mouse brains during fasting.

Impaired brain glucose uptake/metabolism precedes the symptoms of Alzheimer disease (AD) and is likely to play a role in the development of the disease, but the mechanism by which it contributes to AD is not understood. Because glucose uptake/metabolism regulates protein O-GlcNAcylation, and the latter modulates phosphorylation of tau inversely, we investigated, in fasting Kunming mice, whether impaired brain glucose uptake/metabolism causes abnormal hyperphosphorylation of tau and, consequently, facilitates the neurofibrillary degeneration of AD via down-regulation of tau O-GlcNAcylation. We found that fasting caused decreased tau O-GlcNAcylation and concurrent hyperphosphorylation of tau at most of the phosphorylation sites studied. The hippocampus was found more vulnerable to the tau alterations than the cerebral cortex, which is consistent with the fact that it is the hippocampus that is first affected in AD. Furthermore, hyperphosphorylation of tau induced by fasting was reversible in the brain after re-feeding. These findings provide a novel mechanism explaining how impaired brain glucose uptake/metabolism contributes to AD and suggest that it may be feasible to treat AD by reversing the abnormal hyperphosphorylation of tau at early stages of the disease.

Acylation↗
PubMed2006

Crystal structures of Nipah and Hendra virus fusion core proteins.

The Nipah and Hendra viruses are highly pathogenic paramyxoviruses that recently emerged from flying foxes to cause serious disease outbreaks in humans and livestock in Australia, Malaysia, Singapore and Bangladesh. Their unique genetic constitution, high virulence and wide host range set them apart from other paramyxoviruses. These characteristics have led to their classification into the new genus Henpavirus within the family Paramyxoviridae and to their designation as Biosafety Level 4 pathogens. The fusion protein, an enveloped glycoprotein essential for viral entry, belongs to the family of class I fusion proteins and is characterized by the presence of two heptad repeat (HR) regions, HR1 and HR2. These two regions associate to form a fusion-active hairpin conformation that juxtaposes the viral and cellular membranes to facilitate membrane fusion and enable subsequent viral entry. The Hendra and Nipah virus fusion core proteins were crystallized and their structures determined to 2.2 A resolution. The Nipah and Hendra fusion core structures are six-helix bundles with three HR2 helices packed against the hydrophobic grooves on the surface of a central coiled coil formed by three parallel HR1 helices in an oblique antiparallel manner. Because of the high level of conservation in core regions, it is proposed that the Nipah and Hendra virus fusion cores can provide a model for membrane fusion in all paramyxoviruses. The relatively deep grooves on the surface of the central coiled coil represent a good target site for drug discovery strategies aimed at inhibiting viral entry by blocking hairpin formation.

Amino Acid Sequence↗
PubMed2006

Characterization of genes associated with different phenotypes of human bladder cancer cells.

To identify genes associated with morphological phenotypes of human bladder transitional cell carcinoma, we used suppression subtractive hybridization (SSH) to create a subtractive cDNA library of two established cell lines, BLZ-211 and BLS-211, derived from a patient with transitional cell carcinoma of the bladder, then to screen for differentially expressed genes. Real-time reverse transcription-polymerase chain reaction was used to further confirm the selected differentially expressed genes. Forward and reverse subtractive cDNA libraries yielded 168 and 305 putative clones, and among them more than 90% contained the inserts. After differential screening, 36 different transcripts were obtained from 64 cDNA clones of a forward and reverse subtraction library. Among them, 17 were identified as known genes by homology, for example, Vimentin, Keratin7, DDH and UCH-L1. The remaining 19 were unknown expressed genes, and were collected as new expressed sequence tags by the GenBank dbEST database. Their function will be studied further. Thus, SSH appears to be a useful technique for identifying differentially expressed genes between cell lines or clones. Our results, as revealed by SSH, also suggest that differences in gene expression of cytoskeletal proteins might contribute to the different morphologies in BLZ-211 and BLS-211 cells.

Base Sequence↗
PubMed2006

[Expression, structure prediction and functional analysis of murine single-chain fragment variable antibody against human cervical cancer].

OBJECTIVE: To amplify and express the gene encoding murine single-chain fragment variable (scFv) antibody against human cervical cancer and predict the secondary structure and three-dimensional structure of the antibody. METHODS: The gene fragments coding for the variable region of the heavy and light chains of scFv antibody against human cervical cancer were amplified respectively using recombinant DNA techniques from CsA125 hybridoma cells, and spliced together using a flexible linker to the antibody. The scFv genes were then cloned into the expression vector pCANTAB 5E and expressed in E.coli HB2151 and TG1, respectively. The scFv antibody obtained was assayed using SDS-PAGE, Western blotting, and immunohistochemical analysis, with its secondary structure and three-dimensional structure predicted with Swiss-model and 3dpssm. The physicochemical properties of the antibody were analyzed with Antheprot software. RESULTS: The expressed scFv antibody was soluble and phage-displayed. The specific binding capacity of the soluble and phage-displayed scFv antibody to the surface-associated antigen of human cervical cancer cell line were further confirmed. The scFv antibody had a relative molecular mass of 32,000 as was consistent to theoretical prediction, with pI of 7.215 and characterized to belong to alpha+beta protein. The antibody contained many protein kinase C phosphorylation sites and casein kinase II phosphorylation sites in both the VH and VL domains. Computer graphic modeling indicated that the linker was isolated from the VH and VL domains, which formed a hydrophobic pocket in the molecule to facilitate antigen binding. CONCLUSIONS: The soluble and phage displayed scFv antibody expressed in E. coli against human cervical cancer shows high and specific affinity to the cervical cancer cell line surface-associated antigen. The construction and analysis of the molecular model of the antibody may facilitate further studies in engineering of the antibody and exploration of the mechanism of the antigen-antibody interaction.

Amino Acid Sequence↗
PubMed2006

[Changes in cyclooxygenase gene expression during spontaneous recovery from stress ulcer in rats].

OBJECTIVE: To observe the changes in gene expression of cyclooxygenase (COX) during spontaneous recovery from stress ulcer in rats exposed to water immersion and restraint stress (WRS). METHODS: A rat model of stress ulcer was established by means of WRS, in which the changes in COX expression were detected with immunohistochemistry and reverse transcription (RT)-PCR. RESULTS: Very low levels of COX-2 expression were detected in the gastric mucosa of the control rats, and the expression increased significantly during the healing process of the stress ulcer (P<0.05). COX-1 expression in the gastric mucosa showed no significant difference between the control group and the stress ulcer groups during healing (P>0.05). CONCLUSION: COX-1 and COX-2 expressions in rat gastric mucosa during the recovery from stress ulcer participate in the recovery of the damaged mucosa possibly by mediating prostaglandin secretion.

Animals↗
PubMed2006

[Effects of peroxisome proliferators PFOA on immune system of mice].

AIM: To examine the effects of peroxisome proliferators (PP), perfluorooctanoic acid (PFOA), on mouse immune system. METHODS: Male C57B/6 mice were received the diet containing PFOA and the following parameters were examined, including weight and cell number of thymus and spleen, cell cycle of thymocytes by PI staining, cell phenotype in thymus and spleen by flow cyto metry (FCM) analysis, IgM and IgG production by the protein-A plaque and ELISA assay, and proliferation of splenocytes in response to ConA or LPS by (3)H-TdR labeling. RESULTS: Severe thymic and splenic atrophy was observed in mice administrated with potent PP, e.g., PFOA. Number of both T and B cells in spleen was decreased upon treatment. Thymocytes were decreased over 90% by treatment, among which the immature CD4(+) CD8(+) population was decreased most dramatically. The most obvious change in thymocytes occurred in the S and G2/M phases. PFOA also prevented the increase both in plaque formation by anti-IgM and -IgG and in serum level of IgM and IgG that normally evoked by immunization with horse red blood cells. Following withdrawal of PFOA from diet, the above parameters rapidly returned to normal. CONCLUSION: Potent PP significantly inhibits mouse immune system.

Animals↗
PubMed2006

[Screening and identification of heterogeneous phenotype-associated genes in human bladder cancer].

OBJECTIVE: To screen and identify heterogeneous phenotype-associated genes of human bladder transitional cell carcinoma. METHODS: Subtractive cDNA libraries was established by means of suppression subtractive hybridization (SSH) on the basis of two human bladder transitional cell carcinoma cell lines (BLZ-211 and BLS-211) derived from the same patient, which had similar changes in chromosomes but different cell phenotypes (in terms of cell shape, susceptibility to 5-Fu and tumorigenic capacity). The positive clones in the library were selected for screening differentially expressed gene fragments by sequence analysis and blasting, and Northern blotting was performed to confirm the differentially expressed genes. RESULTS: The subtractive forward and reverse cDNA libraries consisted of 168 and 206 white clones containing 200-700 bp inserts. After differential screening, 55 cDNA clones containing 35 different transcripts were obtained, among which 15 were identified by homology analysis as known genes (such as those coding for vimentin, keratin 7, dihydrodiol dehydrogenase and thioredoxin reductase), 11 as unknown genes, and 9 as new ESTs (GenBank dbEST database accession number DY505708, DY230447-8, DR008207). CONCLUSION: SSH is a powerful method for identifying differentially expressed genes between different cell lines or clones, and characterization of the identified genes may provide useful information for understanding the genes responsible for different cell phenotypes.

Blotting, Northern↗